This invention relates to electromechanical systems and techniques for fabricating microelectromechanical and nanoelectromechanical systems; and more particularly, in one aspect, to fabricating or manufacturing microelectromechanical and nanoelectromechanical systems having microstructures encapsulated in a relatively stable, controlled pressure environment to provide, for example, a predetermined, desired and/or selected mechanical damping of the microstructure.
Microelectromechanical systems (“MEMS”), for example, gyroscopes, resonators and accelerometers, utilize micromachining techniques (i.e., lithographic and other precision fabrication techniques) to reduce mechanical components to a scale that is generally comparable to microelectronics. MEMS typically include a mechanical structure fabricated from or on, for example, a silicon substrate using micromachining techniques.
In order to protect the delicate mechanical structure, MEMS are typically packaged in, for example, a hermetically sealed metal container (for example, a TO-8 “can”, see, for example, U.S. Pat. No. 6,307,815) or bonded to a semiconductor or glass-like substrate having a chamber to house, accommodate or cover the mechanical structure (see, for example, U.S. Pat. Nos. 6,146,917; 6,352,935; 6,477,901; and 6,507,082). In this regard, in the context of the hermetically sealed metal container, the substrate on, or in which, the mechanical structure resides may be disposed in and affixed to the metal container. In contrast, in the context of the semiconductor or glass-like substrate packaging technique, the substrate of the mechanical structure may be bonded to another substrate whereby the bonded substrates form a chamber within which the mechanical structure resides. In this way, the operating environment of the mechanical structure may be controlled and the structure itself protected from, for example, inadvertent contact.
When employing such conventional packaging techniques, the resulting MEMS tend to be quite large due primarily to packaging requirements or constraints. In this regard, conventional MEMS packaging techniques often produce finished devices that are quite large relative to the small mechanical structure. In the context of packaging in a metal container, this is due to the size of the container itself since it is quite large relative to the mechanical structure. Where the MEMS employs a substrate packaging technique, the substrate on or in which the mechanical structure resides must have a sufficient periphery to permit or facilitate the two substrates to be bonded using, for example, epoxy, fusion, glass frit or anodic techniques. That periphery tends to significantly increase the size of the resulting MEMS.
The operation of the MEMS depends, to some extent, on the environment in which the mechanical structure is contained and is to operate (for example, the pressure within the metal container). MEMS such as accelerometers tend to operate more effectively in high damping environments whereas gyroscopes and resonators tend to operate more effectively in low damping environments. Accordingly, the mechanical structures that comprise the accelerometer are often packaged in a high pressure environment. In contrast, the mechanical structures that comprise gyroscopes and resonators are often packaged and maintained in a low pressure environment. For example, when gyroscopes and resonators are packaged in a metal container, the pressure in the container is reduced, and often the ambient gases are substantially evacuated, prior to sealing.
There is a need for MEMS (for example, gyroscopes, resonators, temperature sensors and/or accelerometers) that (1) overcome one, some or all of the shortcomings of the conventional packaging techniques and (2) include a controlled or controllable environment for proper, enhanced and/or optimum operation of the mechanical structures.